Anderson was replaced by Franklin Morales in the fourth inning after allowing just one hit on 33 pitches. Chicago beat Colorado 6-5 in 12 innings, dropping the Rockies to 44-68, the worst record in the National League.

"Not real good. His back locked up and he doesn't look too good right now," Rockies manager Walt Weiss said. "It looks like we're going to lose him again for a bit."

Anderson, who is listed as day-to-day, returned to the Rockies rotation on July 13 after missing two months with a broken left index finger. He had a 1-1 record with a 2.84 ERA and 22 strikeouts in five starts with since returning from the disabled list.